The present invention relates to a method and to a measuring instrument for identifying the diffusion length of minority charge carriers and of their topical fluctuations for non-destructive detection of flaws and impurities in a semiconductor crystal body.
For qualitative characterization of the material of a semiconductor crystal, it is known to identify the diffusion length of the minority charge carriers therein since this is valid measurement of the number of recombination centers and traps in the semiconductor crystal. Two methods are standard for identifying the diffusion length of the minority charge carriers in a semiconductor crystal, measuring photoconductivity (photoconductive decay) and measuring the surface photovoltage. Both methods are disclosed in the text "Library of Congress Cataloging" in "Publication Data of Texas Instruments Elec. Ser.", edited by Tyler G. Hicks and Lester Strong, 1975, pages 105 through 129.
In measuring the photoconductivity, the semiconductor is irradiated with light such that electron hole pairs are generated and the change in conductivity is subsequently measured. The life time and, thus, the diffusion length of the minority charge carriers are capable of being identified therefrom. The shape of the semiconductor crystal is thereby of significance for the measurement and the semiconductor crystal must usually be destroyed before the measurement.
A surface photovoltage occurs when a semiconductor crystal is irradiated and can be measured by capacitative coupling. The surface photovoltage can be used to measure the diffusion length of the minority charge carriers. This method, however, has the disadvantage of a long measuring time since measurements with different light wavelengths must be successively carried out. Further, the topical resolution of the measurement is low since the irradiated area must have a size of at least 1 cm.sup.2.